The main thrust of our research for the next year will be: (a) Confirmation that near-ultraviolet irradiation (NUV) in the presence of hydrogen peroxide (H2O2), produces crosslinks of protein with DNA in biological systems. (b) Identification of the specific amino acid(s) and base(s) that crosslink: (1) The main experiments will be done with bacteriophages T7 and fd. (2) We will move to a bacterial system in which proteins are labeled with 35S-cysteine and 3H-thymidine. (3) Similar experiments will be performed with mammalian cells (mouse fibroblast L929, mouse melanoma strain B16, and a near-UV-sensitive cell line of Chinese hamster cells). (c) Additional experiments will be performed to determine the relationship of damage by thymidine starvation and by near-ultraviolet irradiation. Experiments thus far indicate that the mechanism of damage may be the same. This will be confirmed by looking at specific damages and chromophores such as thiodioxyreductase in which the sulfur group may provide chromophoric sensitivity. (d) We will examine the enzymes that are induced by various damages to DNA by irradiations, including near-ultraviolet irradiation, mutagens and carcinogens. A comparison will be made of mechanisms of damage and repair. Enzymes will be induced, separated by acrylimide gels, compared with each other via various induction systems.